1. Field of the Invention
The present invention relates to a photographing lens, particularly a two group type zoom lens whose front lens group has a negative refractive power.
2. Description of the Prior Art
Zoom lenses whose front lens groups have a negative refractive power may be divided into two classes. In one class, the frontmost lens is positive as disclosed in U.S. Pat. Nos. 4,142,779, 4,147,410, and 4,169,660, and in the other class, the foremost lens is negative as disclosed in U.S. Pat. No. 3,848,969.
In such zoom lenses, the frontmost positive lens of the front group is intended to correct distortion. However, when the zoom ratio is large, and when the image angle in the wide angle position is wide, difficulties tend to arise in correcting distortion and astigmatic aberrations. This arises because in this type of lens, the incident height of the off-axis principal ray striking the positive lens is large, while the power of the air lens formed by the rear surface of the first lens and the front surface of the second lens is also large. Hence, when the distortion of the largest image angle in the wide angle position is adequately corrected, substantial barrel distortion occurs for a middle image angle. On the other hand, when the distortion for a middle image angle is adequately corrected, the astigmatic aberration at the largest image angle becomes too large to be corrected.
Furthermore, in such a zoom system, there is a tendency for the image angle more or less to increase at very close photographic distances. Hence, when the power of the aforementioned air lens is great, the angle at which the ray with the largest image angle emerges from the first lens at a position very close to the end of the wide angle position is abruptly increased. Thus, the diameter of the front lens must be quite large. This is a disadvantage in a compact lens. Moreover, in such a lens, the foremost lens is negative so that the position of the rear principal point of the front group is quite large from the rearmost face of the image end of the front group toward the object end. Therefore, it is necessary to provide a large principal point distance between the front group and the rear group at the extreme wide angle position. This results in a large total length that is inconvenient in a compact system. As a further point, the incident height of the principal ray away from the optical axis upon the lens face is small. Hence, it is difficult to correct the distortion at the end of the wide angle position, at which the largest image angle is as large as 84.degree..